1. Field of the Invention
The present invention relates generally to a radio data communication system, and in particular, to a radio data communication system which provides a data service to a radio terminal by connecting a public land mobile network to a local area network (LAN) connected to the public switched telephone network (PSTN), and a method thereof.
2. Description of the Related Art
A code division multiple access (CDMA) radio data communication system may include, a public land mobile network (PLMN) comprised of a mobile switching center, a base station controller and a base station transceiver subsystem, and an interworking function (IWF) for data service with an Internet protocol (IP) network. In order for a mobile terminal to receive the data service, the base station transceiver subsystem receives radio data transmitted from the mobile terminal and transmits the received radio data to the base station controller.
The base station controller then transmits the received data to the interworking function through the mobile switching center. The interworking function is connected to the IP network to provide the data service. When the mobile terminal receives radio data, the procedure is performed in reverse order. The interworking function, interconnected between the mobile switching center and the IP network, has an interfacing function for the additional data service and performs adaptation functions for data transmission among an iDEN (Integrated Dispatch Enhanced Network), a PSTN, an ISDN (Integrated Services Digital Network) and a packet network.
In particular, the interworking function provides a data service for a radio mobile station, has a rate adaptation function between “64 Kbps PCM (pulse code modulated) data” and “compressed data” of an air interface, has a data modem function for a public phone, and also has a G3 FAXMODEM (Facsimile-Modem) function. Although the interworking function is necessary for the radio data service, it includes four or more separate boards, increasing the overall hardware complexity.
Incorporated by reference herein are: U.S. Pat. No. 5,889,770 to Timo Jokiaho et al. entitled Local Updating For A Packet Switched Data Service In A Mobile Communication System which discusses packet data transfer modes between a mobile station and a special data service center. The packet service center produces an interworking function between the cellular radio network and a separate data network. Data packets are transmitted between a mobile station capable of data transmission and the packet service unit by using a so-called virtual connection. In this case, 1) a circuit-switched connection through the cellular network is only established for the period of time required for transmitting a single packet, or 2) packets are transferred through the cellular radio network on the basis of the address on a data packet according to the node-to-node scheme entirely without a circuit-switched connection by using the network elements of the cellular network as nodes; U.S. Pat. No. 5,903,851 to martin Bäckström et al. entitled Radio Link Short Hold Mode For Mobile Circuit Data Applications which discusses a communication link between a mobile switching center and an external network which is enabled using a connection with an interworking unit that enables data to be transferred between the differing communication protocols of the external network and the public land mobile network including the base station, mobile switching center and mobile station; U.S. Pat. No. 5,896,369 to Markus Warsta et al. entitled Mobile Communication System And A Method For Connecting A Remote Workstation To A Data Communication Network Via A Mobile Communication Network which describes using a special interconnecting computer in conjunction with a mobile exchange to allow a remote workstation to be connected over a radio path for extending the connection to a designation data network; and U.S. Pat. No. 5,973,640 to Keun-Ju Lee entitled Method And Device For Managing Status/Alarm Message of GPS Receiver And Broadcast System Time utilizing a High Capacity IPC Node Board Assembly (HINA).